Abstract

This paper describes studies on the recovery of metals from spent hydro-processing catalyst using mixed acidophilic culture in presence of pyrite. This culture was initially grown in the 9K- medium (absence of 9 g/L Fe(II)) where ferrous sulphate (FeSO4) was replaced by pyrite, and then applied in this bioleaching study. Bacterial action on pyrite catalysed the formation of ferric ion (Fe+3), proton (H+) and sulphate ions (SO4-2) in the solution which leached metals (Ni, Mo and V) from the spent catalyst. Experiments were conducted by varying the reaction time, amount of spent catalyst and pyrite, and temperature. After 7 days with 30 g/L of spent catalyst and 50 g/L of pyrite, the leaching of Ni, V and Mo into the solution was 85, 92 and 26%, respectively. With increasing spent catalyst loading, the extent of metal dissolution was decreased, probably due to the precipitation of Fe+3 as a residue. Under all conditions tested, Mo showed recovery due to its precipitation with leach residues as MoO3 observed by applying EDAX and XRD techniques to the leach residues.